The present invention concerns a stepping motor unit for driving two movable elements independently of each other. These elements may be particularly but not exclusively, two time information display elements in an electronic timepiece.
Electronic timepieces with mechanical elements for displaying time information, such as hands or indicator discs, generally comprise a motor coupled to display elements by a gear train. The motor is generally a stepping motor whose rotor comprises a permanent magnet magnetically coupled to a winding by means of a stator. An electronic actuating circuit applies periodic pulses to the winding and the rotor advances by one step, that is to say, generally half a revolution, for each of the pulses applied.
Most of such motors are intended to rotate only in one direction. Sometimes however, it is desired that the motor be capable of rotating in both directions, in particular to facilitate setting the time on the watch. A particular arrangement of the actuating circuit, described for example in U.S. Pat. No. 4,112,671, permits rotation in both directions of a motor which is intended normally to rotate only in one direction. There are also bi-directional or reversible motors such as that described in Swiss Pat. No. 616,302 which are designed to rotate in both directions.
Certain timepieces, in particular that described in Swiss Pat. No. 613,837, are provided with two reversible motors. One of those motors drives for example the elements for displaying seconds and minutes, while the other drives the elements for displaying the hours and the date. Such an arrangement greatly facilitates setting the time displayed by the timepiece and in particular facilitates changing the time zone displayed, which can be effected without the display of seconds and minutes being upset.
The space available in a timepiece and in particular in a wristwatch being severely limited, it is difficult to house two motors therein. In addition, as the motors are relatively expensive components, the cost price of the watch is increased substantitally by the provision of the two motors.